1. Field of the Invention
The present invention relates to a highly hygroscopic laminate for packaging works of art, fur pieces, tea, rice or the like, which are highly hygroscopic and whose commercial value is lowered when they absorb moisture, but if a desiccating agent or the like is used, they are damaged and correspondingly lose their commercial value. The above laminate makes it possible to maintain the relative humidity (RH) of these goods at 20 to 40% during the packaging of the same.
2. Description of the Related Art
When expensive articles such as works of art and objects of craft work are stored or transported, it is necessary to maintain a constant humidity within the environment surrounding these articles. As humidity controlling agents (desiccating agents) used for such purposes, there are known, for example, those comprising silica gel, alumina gel, zeolite and/or montmorillonite (see, for example, Japanese Unexamined Patent Publication (hereinafter referred to as "J.P. KOKAI") Nos. 46-1513, 49-1498 and 1-26731); or sheets which comprise a water-absorbing polymeric single substance sandwiched therebetween, for example, pulp sheets (see, for example, J. P. KOKAI Nos. 1-198346 and 1-153034).
Moreover, there has recently been marketed a humidity controlling sheet for silk fabrics which comprises glycerin as a humidity controlling agent, sandwiched between gas-permeable films (see Japanese Examined Patent Publication (hereinafter referred to as "J.P. KOKOKU") No. 1-12539.
The foregoing humidity controlling agents, however, have a poor responsitivity to a change in humidity, and it takes a long time for them to establish a humidity-equilibrium state, and when they absorb a large amount of moisture under a high humidity condition, the absorbed moisture comes into contact with the article to be subjected to humidity control whereby the article is badly damaged. Furthermore, they are generally packed in a bag of a fabric with coarse texture or paper and then put to practical use, and therefore, the places and methods for use of the same are limited and they are apt to be effective only locally.
Moreover, the sheets between which the water-absorbing polymer is sandwiched have an excellent water absorption power, but a poor moisture absorption power, and therefore, are not practically acceptable.
Accordingly, it is impossible to maintain a relatively low humidity (RH ranging from 20 to 40%), preferable for the foregoing articles such as works of art, within the environment surrounding the articles, when humidity controlling agents and, gas permeable films such as Japanese paper and water-absorbing polymers are independently employed as a single substance. Further, even if a combination of these materials, i.e., the foregoing humidity controlling agents (desiccating agents), Japanese paper or the like and the water-absorbing polymers, is adopted, the method of use and the sustaining of their desired functions are limited, and therefore, they cannot solve the foregoing problems.
Further, the sheet in which glycerin is used as a humidity controlling agent can control humidity in an environment or an article in the range of from 40 to 50% (RH), and correspondingly cannot control it in an RH range of from 20 to 40%, which is preferable for the foregoing articles.